1. Field of the Invention
The present general inventive concept relates to an image forming apparatus and a method of controlling the same, and more particularly, to an image forming apparatus to control a velocity of a printing medium-feeding motor capable of transferring a printing medium, and a method of controlling the same.
2. Description of the Related Art
With the increasing resolution of inkjet printers, there is a need to reduce a transfer error of a printing medium, such as paper.
When transferring the printing paper, the inkjet printer picks up the printing papers loaded in a paper cassette one by one, prints data on the printing medium, and discharges the printed printing medium. The printing medium is transferred along a transfer path by a printing medium-transferring unit receiving the power from a printing medium-feeding motor. Control of the printing medium-feeding motor is important to feed the printing medium.
When driving the printing medium-feeding motor, the deceleration of the motor may be divided into a first deceleration interval and a second deceleration interval to precisely transfer the printing medium. In some instances, the printing medium-feeding motor is accelerated during a first acceleration interval, stops acceleration during a high-constant-velocity interval, is primarily decelerated during a first deceleration interval, stops deceleration during a low-constant-velocity interval, and is finally decelerated during a second deceleration interval. Therefore, the control process of the second deceleration interval greatly affects the precision of the printing medium-feeding operation.
The velocity of the printing medium-feeding motor is controlled by a Pulse Width Modulation (PWM) signal generated from a controller. The PWM signal is increased or decreased (e.g., by increasing or decreasing the duty cycle of the PWM signal) to compensate for the difference between the velocity command and the real velocity. If the PWM drive signal to the printing medium-feeding motor creates a motor force higher than the static frictional force of the transfer apparatus, the printing medium-feeding motor begins to move, and if the PWM drive signal creates a motor force equal to or higher than the kinetic frictional force, the printing medium-feeding motor continues to move.
When the printing medium reaches a target position, the printing medium-feeding motor should stop feeding the printing medium. However, when the paper reaches the target position, a portion of the PWM signal resulting from the difference between the velocity command and the feedback of the real velocity may continue to be applied to the motor and may undesirably create a force higher than the kinetic frictional force. In this case, the printing medium-feeding motor does not stop moving, and continues to move, such that the printing medium may unavoidably escape from the target position.
A conventional art for solving the above-mentioned problem is shown in FIGS. 1A, 1B, and 1C. The conventional art performs the velocity control process from the acceleration interval to the second deceleration interval before the printing medium reaches the target position. The conventional art clears the PWM signal applied to the printing medium-feeding motor at a specific time A at which the printing medium reaches the target position. However, if the force applied to a gear of the printing medium-feeding motor due to the PWM signal disappears, as shown in FIG. 1C, the printing medium-feeding motor is allowed to rotate in a reverse direction, such that the printing medium does not reach the target position.